1. Field of the Invention
This invention relates to the field of fluid handling and, more particularly, to improvements in so-called "poppet valves" for controlling the flow of a pressurized fluid. More specifically, the invention relates to a poppet valve that is structured to reduce the rate at which debris associated with the fluid flowing through the valve accumulates within the valve's internal architecture and thereby degrades the valve performance.
2. Discussion of the Prior Art
In various medical instruments used to analyze blood and other body fluids, fast-acting "poppet" valves are commonly used to control the flow of small volumes of fluids, such as blood, saline and reagent solutions, between the various work stations of the instrument. In general, such valves comprise an inlet port through which a fluid is presentable to a flow chamber, one or more outlet ports operatively connected to the flow chamber for directing fluid away from the valve, and one or more valving mechanisms for selectively enabling or preventing fluid flow between the valve's flow chamber and it outlet port(s). Typically, each of the valving mechanisms includes a valve seat formed in a wall of the flow chamber, such seat providing an opening through which fluid can escape the confines of the flow chamber, and a movable valving member for quickly opening and closing the valve seat to thereby change the ON/OFF state of the valve. Poppet valves having only one valve seat and two ports (i.e., inlet and outlet ports) are referred to as "two-way" valves, and those having two valve seats and three ports (i.e., one inlet port and two outlet ports) are commonly referred to as "three-way" valves. In a three-way valve construction, fluid enters the inlet port, and is selectively expelled through either one of two outlet ports. Specifically, the particular outlet port through which fluid is expelled is determined by the position of the movable valving member which functions to obstruct fluid flow through one outlet port, while simultaneously permitting fluid flow through the other port. Of course, this state can be reversed by moving the movable valving member to an opposing position. Typically, the positioning of the valving member is accomplished through associated solenoid, pneumatic, or other similarly effective means.
An example of a conventional three-way poppet valve is disclosed by Kloehn in U.S. Pat. No. 5,190,076. As is common of many poppet valves, the Kloehn valve is operated by an axially-movable valve stem which, upon being moved, acts to deflect a pair of flexible diaphragms so as to position them to either permit or obstruct the passage of fluid through one of two valve seats which they respectively overly. Depending on the axial position of the valve stem, one of the diaphragms will be urged against one valve seat so as to effectively obstruct fluid flow therethrough, while the other diaphragm will be slightly separated from the other valve seat so as to enable fluid to be expelled through its associated outlet port.
Another type of poppet valve is that disclosed by Loveless in U.S. Pat. No. 4,026,325. The internal architecture of the Loveless valve differs from that of the Kloehn valve in that fluid flow is controlled by a resilient seal ring secured about the periphery of a plunger that is supported by the valve stem. As the valve stem moves axially, the plunger, and its associated resilient seal ring, moves between a valve-closing position in which the seal ring is pressed against the valve seat so as to obstruct fluid flow, and a valve-opening position in which the seal ring is separated from the valve seat so to enable fluid to pass through the valve seat and exit through an outlet port.
While the above-mentioned valve designs may operate effectively when used to control the flow of purified liquids, both encounter a problem when transmitting fluids containing a significant amount of debris or other material that may come out of a suspension or solution and stick to the mating surfaces of valving elements. In the case of blood, such debris is in the form of protein, lipids, and cell fragments found in the serum, all of which are adhesive in nature and tend to stick on any surface they encounter. In the Kloehn valve, such debris will accumulate on the planar surfaces of the diaphragms and the valve seat, causing a decline in the sealing effect of these mating elements. Similarly, the Loveless valve will experience debris build-up on the sealing ring and valve seats, causing fluid to leak to pass the ring seal prematurely. In both valves, debris build-up is hastened as a result of the particular method employed to introduce fluid into the interior of the valve. In particular, in both the Kloehn and the Loveless valves, fluid is introduced into the valve interior such that a highly turbulent flow pattern is produced, with much of the fluid making "head-on" (i.e., steep angle) contact with the surfaces of the various valving elements, such as the plunger or valve stem, seal ring, or the valve seat; as a result, some of the adhesive debris or particulate matter present in the fluid will attach itself to the surfaces encountered and accumulate thereon. After a period of continued use, accumulation of debris will reach a level where the valve fails to either effectively prevent fluid flow, or enable fluid flow at a desired flow rate. Thus, it would be desirable to provide a valving apparatus of the above type in which the rate at which debris accumulates on the internal mating surfaces is significantly reduced, whereby the mean-time-between-failure is significantly increased.